Metal casting methods are known wherein a ceramic shell mold is externally surrounded and supported by compacted support particulates, such as loose sand, in a container during casting. U.S. Pat. No. 5,069,271 and others describe such a casting method. Other casting methods are known wherein a foam pattern of the article to be cast is coated with a refractory coating and is externally surrounded and supported by compacted support particulates, such as sand, in a container during so-called lost foam casting. U.S. Pat. Nos. 4,085,790; 4,616,689; and 4,874,029 describe such a lost foam casting method.
Compaction of support particulates around the exterior of a ceramic shell mold or foam pattern in a casting flask (container) is a demanding process. First, support particulates such as loose sand must be fluidized and transported into deeply recessed voids about the exterior of the shell mold or foam pattern. To promote free flow, bridging of particulates must be eliminated. Next the particulates must be consolidated to provide structural support for the ceramic shell mold or foam pattern, which can be very fragile depending on shell mold wall thickness and surface characteristics of the refractory coated foam pattern. These two requirements are contradictory.
Simple vibration of the casting flask has been employed in the past to consolidate support particulates over all exterior sections of a mold or pattern. Vibration of the casting flask must be sufficiently rigorous to cause displacement and then consolidation of the support particles, but not so severe as to distort or damage the fragile mold or pattern; another contradictory demand.
To facilitate filling long, narrow channel-shaped voids at the exterior of the shell mold or refractory coated foam pattern, the shell mold or foam pattern has been oriented so that those channel-shaped voids are vertical or near vertical. When this is not possible, most compaction processes deal with the problem by controlling the fill rate of the casting flask. Since only the top fraction of an inch of a free surface of support particulates readily flows, this approach calls for filling the particulates media up to the level of the difficult-to-fill horizontal channel-shaped void and pausing the filling process until the fluidized particulates have a chance to travel to the end of the channel-shaped void. Filling of the casting flask is then resumed until the next hard-to-fill void is reached. Relying on this technique calls for precise vibration and particulates addition, recipes, and accurate fill level control.
Another problem with this approach is that for part of the compaction process the top of the shell mold or foam pattern is supported from above, while the bottom section is partially buried in the vibrating support particulate media and moves with the casting flask. The resulting flexing of the mold or pattern can cause mold or pattern distortion and mold wall cracking or pattern coating cracking.
An attempt to overcome the above problems is described in U.S. Pat. No. 6,457,510 and involves synchronizing four vibrators and altering their direction of rotation and eccentric phase angle relative to each other such that shaking of the casting flask can be altered to induce the support particulates to travel sideways. However, this process needs specific, vibration-vector altering recipes tailored to passage-shaped void geometry. Furthermore, controlled shaking is limited to one plane, perpendicular to the axes of the four vibrators. Finally, this patented compaction process, as well as all other compaction processes, are constantly fighting gravity when attempting to fluidize support media.